The invention relates to a method and a device for folding a paper web onto which a liquid folding adjuvant is applied prior to the folding operation.
The liquid adjuvant applied to aid folding is intended to soften the paper fibers so that the folds are made in a highly accurate manner with a sharp edge with the result that when the folded products are stacked the stack only has a comparatively low height without any substantial extra bulk at the spine or fold of the products. There has already been a proposal to apply cold water taken from the public water supply as a means of aiding folding. However, it has become clear from experience that cold water taken from the piped water supply does not lead to the desired effect more especially in the case of certain problematical papers such as printed and/or sized papers. Furthermore attempts have been made in the past to enhance the effect by the addition to the liquid of chemical additives. However there is then the danger that the paper and/or the ink will be excessively affected by the added chemicals, this leading to a tendency to crumble and/or damage of the printed image. The amount of the added chemicals is therefore very limited and this is a further reason for it not being possible to achieve the desired effect in all cases. Furthermore the amount of added complexity in the equipment may in itself prove prohibitive.